Mr Siri, undersecretary at the Transportation Ministry, is accused by Rome prosecutors of accepting a €30,000 bribe for allegedly seeking to favour businessmen in the renewable energy sector. The 47-year-old denies any wrongdoing, but the scandal prompted Five Stars’ Deputy Premier Luigi Di Maio to demand his resignation.

Shortly afterwards the Italian magazine L’Espresso raised allegations of misbehaviour against one of Five Stars' most high profile figures. The mayor of Rome Virginia Raggi, whose term has been marred by allegations of corruption and a rubbish crisis, was recorded urging the head of the city's rubbish-collection company to modify its budget - an apparent abuse of her powers.

The 40-year-old wrote in a Facebook post that she had exercised no pressure on the manager and said she wanted to avoid the approval of an embellished budget which would have granted additional bonuses to the firm’s managers despite their poor management.

The League's leader Matteo Salvini, who has firmly defended Siri, nevertheless immediately called for Ms Raggi to step down.

Mr Salvini has repeatedly attacked the Rome mayor and her administration, fuelling concern that he plans to force Ms Raggi to quit and so win control of the capital.

League officials were also infuriated by the decision of Transport minister Danilo Toninelli, a Five Star politician, to strip Mr Siri of his responsibilities until his judicial position is clarified.

“Salvini isn’t the only one who’s sick and tired of the Five Stars,” the League’s Edoardo Rixi, deputy minister at the infrastructure ministry, told Italian daily La Repubblica on Friday. “We’re all sick and tired. That’s enough.”

Mr Rixi added that the Five Stars are doing “all they can to make us vote in June,” shortly after May’s European Parliament elections.

Mr Salvini could be tempted to force an early election as recent polls show the League drawing around 33 per cent, against 22 per cent for the Five Stars. But the League’s leader is reluctant to join forces again with his former ally, ex-premier and Forza Italia’s leader Silvio Berlusconi.

“Forget a government crisis! The League only wants to govern well and for a long time in the interest of Italians,” Salvini said on Friday. But he attacked again his government ally: “The crisis is only in Di Maio’s head.”